Gear type fluid motor or pump having fluid pressure compensating means

ABSTRACT

A gear-type fluid pump having a two-part housing with axially aligned major and minor bores formed in each housing part and gears mounted in each bore; the pump also includes pressure compensating means comprising a continuous band located around the housing so as to overlie the line of separation between the housing parts, the band engaging each housing part in fluid sealing relationship, and also including a fluid receiving chamber defined between the band and the housing parts with a passage connecting the fluid receiving chamber with fluid manifold means formed in the housing and communicating with the minor bore.

United States Patent 1 1 Dixon et a1.

1451 Apr. 22, 1975 Related US. Application Data [63] Continuation-impartof Scr. No. 219.814. Jan. 21.

1972. abandoned. which is a continuation of Ser. No. 768.820. Oct. 18.1968. Pat. No. 3.637.333.

130] Foreign Application Priority Data Oct. 23. 1967 Australia 28809/67[52] US. Cl. 418/71; 418/125; 418/156; 418/196 [51] Int. Cl...... F01c21/00; FOlc 19/00; F01c 1/08 [581 Field of Search 418/71. 125. 129. 140.418/156. 196. 104

[561 References Cited UNITED STATES PATENTS 1.287.118 12/1918 Shore418/75 2.918.877 12/1959 Woodcock 418/71 2.923.249 2/1960 Lorenz 418/1043.067.691 12/1962 Wiggcrmann 418/196 3.292.550 12/1966 Gordon 418/1303.306.225 2/1967 Smith 418/131 3.444.819 5/1969 Darwent 418/1963.637.333 1/1972 Dixon et a1. 418/182 FOREIGN PATENTS OR APPLICATIONS450.436 10/1927 Germany 418/71 Prinmry Examiner-John J. VrablikAttorney. Agent. or Firm-Stevens. Davis. Miller & Mosher [57] ABSTRACT Agear-type fluid pump having a two-part housing with axially alignedmajor and minor bores formed in each housing part and gears mounted ineach bore; the pump also includes pressure compensating means comprisinga continuous band located around the housing so as to overlie the lineof separation between the housing parts. the band engaging each housingpart in fluid sealing relationship. and also including a fluid receivingchamber defined between the band and the housing parts with a passageconnecting the fluid receiving chamber with fluid manifold means formedin the housing and communicating with the minor bore.

5 Claims, 13 Drawing Figures PATENTEUAPR22IQ75 SHEET 2 If 5 GEAR TYPEFLUID MOTOR OR PUMP HAVING FLUID PRESSURE COMPENSATING MEANS CROSSREFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part of Ser. No. 2l9.8 l4. filed Jan. 2 l I972. nowabandoned. which is a continuing application of Ser. No. 768.820. filedOct. l8. I968. now US. Pat. No. 3.637.333. issued Jan. 25. 1972.

This invention relates to a fluid motor or pump of the gear type thatis. of the type utilizing two or more meshing gears which function asthe driving or pumping members in a known manner.

Motors or pumps of the above type having a relatively simpleconstruction are generally satisfactory for low pressure work. butproblems have been encountered in designing units suitable for highpressure applications. For example. high pressure units so far availableare usually of extremely complex and/or bulky construction therebyseverely limiting their application.

A common construction of motors or pumps of the above type. includes ahousing composed of several parts and which encloses the gears inrelatively close fitting relationship so as to minimize fluid leakage orslippage between the gears and the adjacent surfaces of those housingparts. In operation however. such motors or pumps are subjected tointernal pressures which are unevenly distributed within the housing sothat the housing parts which should closely fit the gears tend todeflect away therefrom and allow leakage of fluid under pressure withconsequent loss of efficiency.

It is a principal object of the present invention to provide a motor orpump of the above type which is of relatively simple construction andwhich is suitable for high and low pressure applications. A furtherobject of the invention is to provide relatively simple means forovercoming the aforementioned deflection without causing any significantincrease in the weight or cost of the motor or pump.

The following description refers in more detail to these essentialfeatures and further optional features of the invention. To facilitatean understanding of the invention. reference is made to the accompanyingdrawings where these features are illustrated in preferred form. It isto be understood however. that the essential and optional features ofthe invention are not limited to the specific forms of these features asshown in the drawings.

In the drawings:

FIG. I is an end elevational view of one embodiment of the presentinvention. which view is partially sectioned for convenience ofillustration;

FIG. 2 is a cross-sectional view taken along line lI-II of FIG. 1;

FIG. 3 is a fragmentary sectional view taken along line III-III of FIG.2;

FIG. 4 is an enlarged sectional view taken along line IV-IV of FIG. 1;

FIG. 5 is an enlarged sectional view of a portion of the control valvemechanism shown in FIG. 2;

FIG. 6 is a cross-sectional view taken along line VIVI of FIG. 5;

FIG. 7 is an end view of a further embodiment of the invention,partially sectioned for convenience of illustration;

FIG. 8 is a cross-sectional view taken along line VIII- -VIII of FIG.7'.

FIG. 9 is an enlarged fragmentary sectional view taken along line IXIXof FIG. 8, in which view the main gear has been omitted for convenienceof illustratron;

FIG. I0 is an enlarged cross-sectional view taken along line XX of FIG.9;

FIG. II is a fragmentary sectional view of a modified version of theembodiment shown in FIG. 8:

FIG. 12 is a fragmentary sectional view of a further modification of theembodiment shown in FIG. 8', and

FIG. 13 is a cross-sectional view of yet another embodiment of theinvention.

In the particular example shown in FIGS. I to 6. the housing includes anintermediate housing part 2 and two end housing parts 3 and 4. Theintermediate part 2 has formed therethrough a major bore 6 which contains a main gear 7 in closely fitting relationship. and one or moreminor bores 8 located laterally of the bore 6 but communicatingtherewith. Preferably. four minor bores 8 are provided in equally spacedrelationship about the circumference of the major bore 6. Each minorbore 8 contains a pinion gear 9 in closely fitting relationship. and thelateral spacing of the respective axes of the main gear 7 and eachpinion gear 9 is such that the main gear 7 meshes with each pinion gear9 in a known manner.

The housing end parts 3 and 4 are releasably secured by bolts II toopposite ends respectively of the intermediate housing part 2 so as toextend across at least a portion of each of the bores 6 and 8 andthereby limit axial movement of the gears 7 and 9 relative to thehousing. For best results. such axial movement. or more correctly theend clearance for the gears 7 and 9. should be kept to a minimum. In oneform. the gears 7 and 9 each have a length substantially equal to but nogreater than the axial thickness of the intermediate housing part 2, andeach end housing part 3 and 4 has a planar surface which engages arespective end face of the intermediate housing part 2 and defines anend wall for each of the gear cavities formed by the bores 6 and 8.

Inlet and outlet fluid manifolds I2 and 13 respectively may be providedin the housing end parts 3 and 4 as shown in FIG. 2. Alternatively. theinlet and outlet manifolds l2 and I3 may be formed in the same housingpart 3 or 4. It will be appreciated that although manifolds I2 and 13may act as inlet and outlet respectively when the unit is used as -amotor having a drive in one direction. their roles will be reversed whenthe direction of drive is reversed. The same may apply when the unit isused as a pump.

Each minor bore 8 communicates with the inlet and outlet manifoldsthrough ports I0 and I5 respectively. In this regard. see FIGS. 1. 3 and6. Ports I0 are provided in the end part 3. whereas ports I5 areprovided in endpart 4.

A driving or driven member operatively connected to the main gear 7 maybe in the form ofa shaft I4 extending through one end of the housing andthrough an axial bore I6 of the main gear 7. and a quill or hollow shaft17 may be drivably connected to both the shaft I4 and the main gear 7.Such a drivable connection may include internal and external splines 18and I9 respectively on the quill 17 which respectively engage withexternal and internal splines II and 22 on the shaft I4 and main gear 7respectively. The shaft 14 will be driving or driven according towhether the unit is used as a pump or motor respectively.

With the above drive arrangement. each housing end part 3 and 4 ispreferably provided with an open ended bore 23 and 24 respectively whichare in substantial axial alignment with the bore 16 of the main gear 7.An end cap 26 may be attached over the outer end of the bore 24 andlocates within that bore to provide a journal bearing for the adjacentend of the shaft 14. An annular bearing member 27 may be secured to theouter end face of the housing end part 3 to rotatably support portion ofthe shaft 14 extending through that end part.

In order to avoid or at least minimize distortion of the housing. a pairof compensating members are located one within the other about theintermediate housing part 2. The outer surface of the intermediatehousing part 2 is preferably cylindrical in which case the innercompensating member is preferably in the form of a substantiallycylindrical band 28. Nevertheless, the outer periphery of that membermay have any other appropriate shape. although a cylindrical shape isgenerally most convenient to form. The internal diameter of the band 28is predetermined so that it bears against the outer surface of theintermediate housing part 2. and the band 28 preferably extends acrossthe entire width of the outer surface of the intermediate housing part2.

It is further preferred that the band 28 extends beyond the oppositeends of the intermediate housing part 2 so that end portions of itsinner surface bear on cylindrical surfaces 29 and 3t formed on theadjacent end portions of the housing end parts 3 and 4 respectively.

The outer compensating member may be also in the form ofa cylindricalband 32. although that is not necessary. It is only necessary that theouter member has a bore therethrough which is substantiallycomplementary in cross-sectional shape to the outer peripheral shape ofthe inner band 28. so as to bear against the outer surface of that innerband. The outer peripheral shape of the outer member may be of anyconvenient form.

By way of example, the outer member may constitute a casing for themotor or pump housing which serves as mounting and sealing means as wellas fulfilling its primary function as a compensating member. In such anarrangement (not shown). the casing may have a bore therein forreceiving the inner band 28 in close fit ting relationship. and an endwall defining the aforementioned journal bearing for the adjacent end ofthe shaft 14. An annular wall may be removably mounted at the other endof the casing to surround the shaft 14 in fluid sealing relationship sothat the housing parts 2. 3 and 4 are completely enclosed within thecasing. With this particular construction it is not necessary to providethe aforementioned end cap 26 and annular bearing member 27. Also.either one or both of the fluid manifolds may be formed in an end wallof the casing rather than in the housing end parts 3 and 4.

For convenience of description however. the outer compensating memberwill be hereinafter referred to as the outer band 32.

The outer band 32 preferably extends across substantially the full widthof the inner band 28 and engages the outer surface of the inner band 28at least at the end portions thereof. A fluid chamber 33 is preferablyprovided between the adjacent surfaces of the bands 28 and 32. and thatchamber may be formed by a relatively shallow circumferential grooveformed in either or both of those surfaces. Preferably. the groove orchamber 33 is of substantially the same width as the intermediatehousinng part 2 and is disposed in substantial alignment therewith. fora purpose hereinafter made clear. Also resilient 0 rings or otherappropriate sealing means may be provided at or adjacent each side ofthe groove or chamber 33 to prevent or minimize fluid leakage laterallyfrom the chamber 33 between the two bands 28 and 32.

A fluid supply passage 34 may be formed through the inner band 28 andthe intermediate housing part 2 to provide a communication between thefluid manifolds l2 and I3 and the chamber 33. Any appropriate valvemechanism may be employed to control the flow of fluid through thesupply passage 34. That is. the valve mechanism may be operableautomatically or manually to connect the fluid chamber 33 with aselected one of the manifolds l2 and 13. For example. a shuttle valve 36may be employed which will automatically connect the fluid chamber 33 tothe manifold 12 or 13 which is subjected to the highest fluid pressure.and disconnect the chamber 33 from the manifold subjected to the lowerpressure. The valve 36 may connect the chamber 33 to both manifolds l2and 13 if they are subjected to equal pressures. The shuttle valve 36 ispreferably constructed as shown in FIGS. 5 and 6. That is. it isslidably mounted within a lateral passage 37 communicating with passage34, and has tapered head portions 38 each of which is adapted to closean orifice 39 formed in a respective valve plate 41.

In use. both the compensating fluid chamber 33 and the main fluidchamber defined by the gear cavities. usually receive fluid from theinlet manifold l2 so that substantially the same pressure may exist inboth chambers. The pressure within the main chamber tends to force theintermediate housing part 2 radially outwardly and is thereforetransmitted through that housing part to produce a radially outwardthrust against the inner surface of the inner band 28. The pressurewithin the compensating chamber 33 however. produces a radially inwardsthrust against the outer surface of the inner band 28, which inwardthrust may be substantially equal to the aforementioned outward thrustbecause of the substantially equal thrust areas involved.

As there is usually a pressure gradient within the main fluid chamber.there will be zones at which the inward thrust on the inner band 28exceeds the outward thrust thereon. The higher inward thrust however. isusually prevented from causing significant distortion or deflection ofthe inner band 28 because that band bears on the end housing parts 3 and4 which are able to resist relatively high radial forces because oftheir relatively large radial thickness.

Similarly. the outward thrust may exceed the inward thrust at somezones. but the resultant outward force is generally insufiicient tocause deflection of the inner band 28 such as to disturb the efficiencyof the motor or pump. in this regard. the outer band 32 may be ofrelatively heavy section compared to the inner band 28 thereby providinga solid backing member for the inner band 28.

It will be appreciated from the foregoing that the compensating meansdescribed will effectively prevent or reduce deflection or distortion ofthe housing so that fluid loss due to leakage between the housing andthe gears is kept to a minimum over a wide range of pressures. The bulkand weight ofa motor or pump utilizing the compensating means describedmay be considerably less than a motor or pump having a correspondingcapacity and which is otherwise rigid enough to resist deflection ordistortion by use of previously known means.

A motor or pump Incorporating the compensating means described can bepressurized over the outer pe riphery and end faces of the housing andon the inner surface of the main gear, at a pressure which may be lessthan the pressure operating the motor or pump. being regulated at someoptimum proportion of same. Also. a motor or pump so arranged. having aseal on its driven or driving shaft so that leakage of fluid from areasof high pressure and the compensating chamber 33 to areas of lowpressure. will automatically result in a pressure within thecompensating chamber 33 which is directly proportional to the systempressure and which may be made to bear on all or selected areas of thehousing so as to effectively reduce or prevent deflection thereto.

A further problem encountered with motors or pumps of the typedescribed. is that they are relatively expensive to manufacture becauseof their complex construction and the tolerances which must be adheredto in order to obtain efficient operation. One particular cause of thisproblem is the mounting of the gears. and present means for suchmounting involves the use of spindles or stub axles for each gear andwhich are rotatably mounted in appropriate bearings so as to allow therespective gear to turn freely. Such mounting arrangements require thatthe gears be confined to precise centres of rotation in order that theoperating clearance between the gears and the housing can be maintainedsufficiently small and consistent so as to minimize leakage of fluidbetween the gears and the housing.

In addition to the above. such spindles or stub axles and theirrespective bearings. have been rendered indispensable because of theparticular means hitherto adopted for achieving partial balance of thefluid pressure and mechanical loads on the gears. A substantial part ofthe manufacturing cost of such fluid motors or pumps is incurred in theprecise machining operations necessary to locate the spindles or stubaxles and bearings within the housing in appropriate relation to thestationary parts of the motor or pump. That location is of coursecritical so that the respective gears are mounted with sufficientaccuracy to achieve the relatively small working clearances necessaryfor efficient operation.

The foregoing problem is particularly evident in relation to mountingofthe main gear 7. In the construction described. the problem isalleviated by provision of a coupling means for the main gear 7 whichallows misalignment of the respective rotational axes of the main gear 7and the shaft I4. The arrangement is such that the main gear 7 is"floatingly mounted within the major bore 6 so that lateral movement ofthat gear is restricted only by the cylindrical surface of the bore 6.In use however. a film of fluid is formed between the cylindricalsurface of the bore 6 and the crown of the teeth of the main gear 7thereby preventing metal to metal contact between the gear and thatsurface.

The quill I7 functions as the coupling means and is able to tiltrelative to the rotational axis of either the shaft I4 or the gear 7thereby allowing the aforementioned misalignment to occur. The splines18 and I9 of the quill I7 may be manufactured with a backlash tofacilitate tilting of the quill axis as required. It will be appreciatedthat other coupling means such as a Hookes joint or a universal jointmay be used with equal effectiveness.

Turning now to the embodiment of FIGS. 7 to 10, that embodiment is ofparticularly simple construction thereby enabling comparatively economicmanufacture and assembly. One of the principal differences between thisembodiment and that of FIGS. I to 6. is the fact that the housing isconstructed in two main parts. The housing parts 103 and I04 abut in aplane extending normal to the rotational axis of the main gear 107, andare retained in assembly by studs III.

Major and minor bores I06 and I08 communicate as previously described.and in the preferred arrangement there are five minor bores I08. Apinion I09 is provided in each bore 108 so as to mesh with the main gearI07. Each minor bore 108 communicates with inlet and outlet manifolds H2and H3 through ports 110 and IIS respectively. The manifolds H2 and H3are both formed in the end part I04. as are the ports H0 and IIS (seeFIGS. 8 and 9).

The ports I10 and preferably communicate with the minor bores 108through respective shallow grooves 151. A narrow channel 152 may beformed at the end of each groove I51 remote from the respective port asshown in FIG. I0. Such channels I52 have been found useful in preventingor minimizing cavitation.

A further important distinction over the previous embodiment is themounting of the pinion gears I09. As shown in FIG. 8. each minor boreI08 extends completely through the housing parts 103 and 104. althoughit may extend through only one end face of the housing if desired. Theopposite ends of each pinion 109 are secured against relative movementto respective cylindrical bearing members I53. In the embodiment shown.the bearing members 153 are secured to the pinion 109 by screw threads.but any other suitable means may be used. The bearing members 153 arecoaxial with the pinion 109 and have the same outer diameter. and thecomplete pinion assembly is rotatably and slidably located within itsrespective bore I08.

It will be appreciated that the bores 108 are simple to form. and thereis no problem in assembling the pinions I09 within the housing. Eachpinion 109 is retained in its correct axial position by teeth of themain gear 107 locating between and being engageable with adjacent facesof the bearing members I53. Seal caps 154 may be removably retained ineach end of each bore 108 by circlips 156. or any other appropriatemeans.

Pressure compensating means may be provided in this embodiment. In oneform, such means includes at least one. but preferably two cavities I57provided in the housing parts I03 and I04 radially outwardly of eachminor bore 108. Preferably. each cavity I57 is elongated in the axialdirection of the associated pinion I09. and extends for substantiallythe same length as the pinion I09 and is in substantially radialalignment therewith. Although the cavities 157 may have any suitableshape in transverse cross section. they are preferably areuate andgenerally follow the contour of the adjacent bore 108 as shown in FIGS.7 and 9. A passage 134 (see FIG. 8) connects each cavity I57 with theadjacent bore 108.

The embodiment of FIGS. 7 to I also preferably includes a coupling meansas described in relation to the previous embodiment. That is. a quill H7has an outer spline I19 at one end drivably engaging with an innerspline I22 of the main gear I07. An inner spline I18 at the opposite endof the quill ll7 engages a spline I2I formed on a shaft 114. The quillI17 and the main gear 107 function as previously described. Inparticular. the gear 107 is floatingly mounted.

In a modification of the embodiment of FIGS. 7 to I0. as illustrated inFIG. I]. a shaft 114 is not provided but the quill 117 is arranged toaccept the spline for a shaft or any other driving or driven member.Suitable seals I58 and 159 are provided to prevent or minimize fluidleakage. In all other respects. the arrangement is substantially aspreviously described. Such a construction is particularly applicable tomounting direct on a wheel or a winch for example.

A further modification of the FIG. 7 to embodiment is illustrated inFIG. 12. In that modification. the compensating means includes acylindrical band 128 instead of the cavities 157. The band 128 islocated within a recess I61. and a fluid receiving space 133 is definedbetween the inner surface of the band I28 and the base of the recessI61. The inner surface of the band 128 is preferably substantiallycomplementary to the base of the recess so that only a film of fluid isreceivable within the space 133. Seals I60 are provided at the cornersof the recess I6I to prevent or minimize fluid leakage from the space133.

The space 133 is connectable with manifolds I12 and H3 through passagesI62. I63 and I64. A control valve 136 is preferably provided toautomatically conneet the space I33 to the manifold subjected to thehigher pressure. and to automatically disconnect the space 133 from themanifold subjected to the lower pressure. The valve I36 may be of thesame basic construction as the valve 36 described in relation to thefirst embodiment. and consequently has tapered heads I38 operable toclose respective orifices 139. Each orifice 139 is connected to arespective one of the passages I63 and I64.

The housing construction and pinon assembly as described in relation tothe embodiments of FIGS. 7 to I2. have several important advantages. Thehousing construction for example is comparatively simple to manufactureand has a high resistance to distortion compared to a three part housingconstruction as described in relation to the embodiment of FIGS. 1 to 6.Also. manufacturing errors are necessarily reduced because of the smallnumber of parts comprising the housing. For example. the pinion bores108 can be formed after the housing parts I03 and 104 are assembled.thereby enabling a high degree of accuracy.

The pinion assembly enables the use of a two part housing because thebearing members 153 have a common diameter with the pinion body I09. Thebearing members 153 carry radial loads applied to the pinion I09 byhydraulic pressure and tooth loads. and they also resist axial hydraulicforces acting between the pinion teeth thereby relieving the housing ofthose forces. In addition. the members I53 effectively seal the ends ofthe pinion cavity against loss of fluid and also locate the pinion inits correct axial position by close fitting relationship on oppositesides of the main Ill gear 107. Other advantages of such a pinionassembly will be readily apparent to persons skilled in the art.

From the foregoing it is clear that the method of manufacturing thetwo-part housing would include the steps of forming the housing partssuch as by casting and machining the mating surfaces smooth. Pocketswould be formed in each half to define the major bore and (preferably aplurality) minor bores when the housing parts are assembled together. Inprecision casting such as die casting. the machining can be eliminatedor minimized and the forming of an opening completely through onehousing half could be part of the precision casting or a separate step.As previously stated. the axes of the minor bores are substantiallyparallel to the axis of the major bore and are located radially outwardsjust a sufficient distance so that the pinions will mesh with the maingear.

The pinions may. of course. be mounted on various types of bearing meanssuch as a cylindrical bearing or a shaft fixed to the housing such asbeing secured to the end bearing members which are in turn secured to arespective housing part against relative movement. such as by a pressfit or by fastening screws. The securing means for the shaft can be aseal cap mounted. preferably removably. in the opening which was formedfor the making of the minor bore. With a fixed shaft various types ofbearings may be used such as a needle hearing within the pinion if theshaft extends through the pinion or the pinion can be supported on twostub shafts which extend from cylindrical bearings as previouslydescribed.

Yet another embodiment of the invention is illustrated in FIG. 13. Theprincipal and important distinction of this embodiment is the housingconstruction. All other components are substantially as described inrelation to the first embodiment. and consequently will be given passingreference only.

The housing includes an intermediate part 202 and end parts 203 and 204which are substantially as described in relation to the firstembodiment. Those parts however. are contained within a bore 266 of acasing having a skin 232 and an end wall 267 which closes one end of thebore 266. Axial movement of the parts 202. 203 and 204 within the bore266 is restricted by a retainer plate 268 which is releasably lockedwithin the open end of the bore 266 by an annular nut 269.

A plurality of pinions 209 (five for example) are rotatably mountedwithin the housing and mesh with a main gear 207. Each pinion 209 mayhave its opposite end portions rotatably mounted in respective end parts203 and 204 by needle bearings or any other suitable means. A quill 2I7drivably connects the main gear 207 to a shaft 214 in the mannerpreviously described so that the main gear 207 is "floatingly mounted.Manifolds 212 and 213 may be provided within the casing end wall 267.

Compensating means is provided and preferably includes a cylindricalband 228 which contains the housing parts 202, 203 and 204 and engagesan outer cylindrical surface of each one of those parts. The band 228 isinterposed between the aforementioned housing parts and the skirt 232 sothat the skirt functions as the outer band 32 of the first embodimentdescribed. and a fluid receiving space 233 is defined between the band228 and the skirt 232. The outer surface of the band 228 is preferablysubstantially complementary to the surface of bore 226 so that only afilm of fluid is receivable within the space 233.

Fluid from the major and minor bores (not shown) of the housing isconveyed to the space 233 by passing between the adjacent surfaces ofplate 268 and end part 203 and the adjacent surfaces of wall 267 and endpart 204. The fluid pressure between those surfaces and in the space 233is usually substantially the mean of the respective pressures acting inthe manifolds 2l2 and H3. Thus, during use, the housing parts 202, 203and 204 are completely encapsulated in pressurized fluid therebyminimizing distortion or deflection of those parts.

A shallow groove 271 may be formed in the outer cylindrical surface ofthe intermediate part 202 so as to allow limited radially inwarddeflection of the band 228. Preferably, that groove 271 communicateswith atmosphere through passages 272, 273 and 274.

It will be appreciated that a casing as described in relation to thelast embodiment, may be used with any one of the previous embodiments.Furthermore. the compensating means described in relation to the variousembodiments has the important advantage of enabling manufacture of acompact unit in which fine clearances may be provided between the gearsand the casing. in particular, the compensating means avoidsfi'ilitortion of the housing such that the pinions foul with t irrespective surrounding cavity wall.

Having now described our invention. what we claim as new and desired tosecure by letters patent is:

l. A fluid motor or pump of the gear type including a housing having amajor bore and at least one minor bore formed therein. the axes of thesaid bores being substantially parallel and being relatively disposed sothat said minor bore communicates with said major bore; said housingbeing formed as two parts which are assembled in face to facerelationship along a plane extending normal to the axes of said boresand located between axially opposite ends of the major bore: said majorbore being defined by a pair of axially aligned cylindrical pockets eachof which is formed in a respective one of said housing parts; a maingear rotatably mounted within said major bore; a pinion gear rotatablymounted within said minor bore and meshing with the main gear; fluidmanifold means formed in said housing and communicating with said minorbore; and presure compensating means located radially outwards of saidminor bore so that a portion of said housing is interposed between saidpressure compensating means and said minor bore. said pressurecompensating means including a continuous band located around saidhousing so as to overlie the line of separation between said housingparts; said band engaging each said housing part in fluid sealingrelationship, and a fluid receiving chamber defined between said bandand said housing parts. said pressure compensating means being arrangedto receive pressurized fluid and thereby apply a radially inwardlydirected force to said housing portion to minimize radially outwarddeflection thereof.

2. A fluid motor or pump according to claim 1 wherein passage meansconnects said fluid receiving chamber with said fluid manifold means.

3. A fluid motor or pump according to claim I, wherein said minor boreextends to at least one of the two axial end faces of said housing. apair of cylindrical bearing members support respective opposite ends ofsaid pinion within said minor bore so as to rotatably mount said pinionwithin said housing. and at least that part of said bearing memberadjacent the pinion has an outside diameter substantially equal to thatof the said pinion.

4. A fluid motor or pump according to claim I wherein said band islocated within a recess formed within the radially outer surface of saidhousing parts. said fluid receiving chamber is defined between theradially inner surface of said band and the base of said recess. and theradial thickness of said chamber is small by comparison with the axiallength thereof so that only a thin film of fluid is receivable withinsaid chamber.

5. A fluid motor or pump according to claim 4. wherein said fluidreceiving chamber is connected to said fluid manifold means through avalve mechanism which is operable to automatically connect said chamberwith that part of the manifold means which is subjected to the higherpressure and to prevent communication between said chamber and that partof the manifold means which is subjected to the lower pressure.

1. A fluid motor or pump of the gear type including a housing having amajor bore and at least one minor bore formed therein, the axes of thesaid bores being substantially parallel and being relatively disposed sothat said minor bore communicates with said major bore; said housingbeing formed as two parts which are assembled in face to facerelationship along a plane extending normal to the axes of said boresand located between axially opposite ends of the major bore; said majorbore being defined by a pair of axially aligned cylindrical pockets eachof which is formed in a respective one of said housing parts; a maingear rotatably mounted within said major bore; a pinion gear rotatablymounted within said minor bore and meshing with the main gear; fluidmanifold means formed in said housing and communicating with said minorbore; and presure compensating means located radially outwards of saidminor bore so that a portion of said housing is interposed between saidpressure compensating means and said minor bore, said pressurecompensating means including a continuous band located around saidhousing so as to overlie the line of separation between said housingparts; said band engaging each said housing part in fluid sealingrelationship, and a fluid receiving chamber defined between said bandand said housing parts, said pressure compensating means being arrangedto receive pressurized fluid and thereby apply a radially inwardlydirected force to said housing portion to minimize radially outwarddeflection thereof.
 1. A fluid motor or pump of the gear type includinga housing having a major bore and at least one minor bore formedtherein, the axes of the said bores being substantially parallel andbeing relatively disposed so that said minor bore communicates with saidmajor bore; said housing being formed as two parts which are assembledin face to face relationship along a plane extending normal to the axesof said bores and located between axially opposite ends of the majorbore; said major bore being defined by a pair of axially alignedcylindrical pockets each of which is formed in a respective one of saidhousing parts; a main gear rotatably mounted within said major bore; apinion gear rotatably mounted within said minor bore and meshing withthe main gear; fluid manifold means formed in said housing andcommunicating with said minor bore; and presure compensating meanslocated radially outwards of said minor bore so that a portion of saidhousing is interposed between said pressure compensating means and saidminor bore, said pressure compensating means including a continuous bandlocated around said housing so as to overlie the line of separationbetween said housing parts; said band engaging each said housing part influid sealing relationship, and a fluid receiving chamber definedbetween said band and said housing parts, said pressure compensatingmeans being arranged to receive pressurized fluid and thereby apply aradially inwardly directed force to said housing portion to minimizeradially outward deflection thereof.
 2. A fluid motor or pump accordingto claim 1 wherein passage means connects said fluid receiving chamberwith said fluid manifold means.
 3. A fluid motor or puMp according toclaim 1, wherein said minor bore extends to at least one of the twoaxial end faces of said housing, a pair of cylindrical bearing memberssupport respective opposite ends of said pinion within said minor boreso as to rotatably mount said pinion within said housing, and at leastthat part of said bearing member adjacent the pinion has an outsidediameter substantially equal to that of the said pinion.
 4. A fluidmotor or pump according to claim 1 wherein said band is located within arecess formed within the radially outer surface of said housing parts,said fluid receiving chamber is defined between the radially innersurface of said band and the base of said recess, and the radialthickness of said chamber is small by comparison with the axial lengththereof so that only a thin film of fluid is receivable within saidchamber.